1. Field of the Invention
The present invention relates to a microwave oven, and more particularly to a microwave oven employing a klystron for achieving lightness and eliminating a danger due to high voltage.
2. Description of the Prior Art
Typically, microwave ovens employ a magnetron which is energized with a high voltage of, for example, 4 KV. For using such a magnetron, the microwave ovens needs a high voltage transformer which results in a problem in safety, an increase in weight, and an increase in manufacture cost.
An example of such a microwave oven employing the magnetron is illustrated in FIG. 1.
In FIG. 1, the reference numeral 10 denotes a power supply unit including a high voltage transformer and a high voltage condenser. As a user manipulates a control panel (not shown) arranged at the right portion of a front surface of the microwave oven, the power supply unit supplies electric power to a magnetron denoted by the reference numeral 20 in FIG. 1 and a cooling fan not shown. The magnetron 20 is activated upon receiving a high voltage of 4 KV from the power supply unit 10. At the activated state, the magnetron 20 emits microwaves via an antenna 22. The microwaves emitted from the antenna 22 of magnetron 20 are guided to a cooking chamber 50 via a wave guide 30 and then spread in the cooking chamber 50 by a stirrer 40. The spread microwaves are incident on a food contained in the cooking chamber 50, so that cooking can be carried out.
On the other hand, the cooling fan (not shown) is typically arranged behind the magnetron 20 when viewed in FIG. 1. The cooling fan generates wind for cooling the magnetron 20. As the wind cools the magnetron 20, the wind increases in temperature. The heated wind is guided to an inlet 70 by a duct (not shown) so that it can be introduced into the cooking chamber 50.
The inlet 70 is constituted by at least one aperture having a diameter l less than 1/4 of the wavelength .lambda. of microwaves (l&lt;.lambda./4) so as to prevent the incident microwaves from being leaked through the aperture.
In FIG. 1, the reference numeral 60 denotes a housing as an enclosure of the microwave oven.
FIG. 2 is a sectional view illustrating the magnetron 20 of the microwave oven shown in FIG. 1. As shown in FIG. 2, the magnetron 20 is a cylindrical bi-pole vacuum tube. At the center of magnetron 20, a cathode 22 is arranged. When an operating voltage is applied to an input terminal 21, the cathode 22 is heated to emit electrons. Arranged around the cathode 22 is an anode 23 which receives electrons emitted from the cathode 22.
A pair of cylindrical magnets 24a and 24b are disposed above and beneath the magnetron 20. The magnets 24a and 24b generate magnetic fluxes which are, in turn, guided by guide members 25a and 25b to pass through a cavity 26 defined between the cathode 22 and anode 23 and kept in vacuum.
Accordingly, the electrons emitted from the cathode 22 are deviated by a magnetic field formed in the cavity 26, so that they may revolve between the cathode 22 and the anode 23.
Where a lot of electrons revolves in groups in the cavity 26, a resonance circuit is constructed in the anode 23. By this resonance circuit, microwaves are generated. The anode 23 which is increased in temperature due to impact among electrons is cooled by cooling fins 29. The microwaves are outputted at the antenna 27 connected at one end to the anode 23.
The antenna 27 is protrudes upwards through a hole centrally provided in the upper magnet 24a . The protruded portion of antenna 27 is capped with a cap 28. That is, the cap 28 is mounted to surround the antenna 27.
The microwaves, namely, radio frequency waves emitted from the antenna 27 reach the cooking chamber via the wave guide and the inlet both typically equipped in conventional microwave ovens and then heat the food contained in the cooking chamber.
However, since a high voltage of about 4 KV should be applied between the cathode 22 and the anode 23 in the magnetron having the above-mentioned construction, the conventional microwave oven encounters a problem in safety. Moreover a heavy transformer and condenser are required for generating the high voltage. As a result, the conventional microwave oven is bulky and heavy. In addition, an increase in manufacture cost is involved.